Selective feeding byAbarenicola pacificawith notes onAbarenicola vagabundaand a concept of gardening in lugworms

Abstract Abarenicola pacifica ingests quantities of sediment but, normally, diatoms and most bacteria forming a surface film on ingested sand grains and fragments of algae pass the gut undigested. Ciliates, flagellates, small nematodes and some bacteria in the interstitial water are digested. The nutritionally important material is associated with particles passing a 80 µm sieve. This material is selected for. Pauses in feeding occur and A. pacifica voids highly variable amounts of feces. Due to selective feeding for fine particles and organic matter in the sediment, the feces of A. pacifica is constantly richer in organic components than the sediment surrounding the worm. Only the concentration of protein, calculated as per cent of the total organic matter, is higher in front of the worm than in the feces. On basis of the high values of protein and the distribution of microorganisms in artificial lugworm burrows, a concept of gardening is introduced. This implies that A. pacifica enriches the sediment by stimulating growth of digestible microorganisms. The irrigation and feeding behaviour of A. pacifica significantly increase the mineralization of detritus not digested by the worm. A comparison with Abarenicola vagabunda indicates that this species apparently utilizes the microorganisms of the surface film of sand grains to a higher degree than A. pacifica.